Protocol data units and header in multihop relay network

ABSTRACT

The invention provides a data structure embodied in a computer readable media. The data structure is a protocol data packet (PDU) communicated in a mobile multihop network between stations. The data structure includes a relay media access header, a payload and an optional cyclical redundancy checksum for the protocol data unit, and an indication whether the PDU is a relay media access protocol data unit or not.

RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/770,327filed on Jun. 28, 2007 now U.S. Pat. No. 8,165,058, entitled “ProtocolData Units and Header in Multihop Relay Network,” by Zhifeng Tao whichclaims priority to U.S. Provisional Patent Application 60/892,362, filedon Mar. 1, 2007. Both applications are incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates generally to wireless communication networks, andmore particularly to protocol data units in mobile multihop relaynetworks.

BACKGROUND OF THE INVENTION

Orthogonal frequency-division multiplexing (OFDM) is a modulationtechnique used at the physical layer (PHY) of a number of wirelessnetworks, e.g., networks designed according to the IEEE 802.11a/g, andIEEE 802.16/16e standards. OFDMA is a multiple access scheme based onOFDM. In OFDMA, separate sets of orthogonal tones (subchannels) and timeslots are allocated to multiple transceivers (users) so that thetransceivers can communicate concurrently. As an example, the IEEE802.16/16e standard has adopted OFDMA as the multiple channel accessmechanism for non-line-of-sight (NLOS) communications at frequenciesbelow 11 GHz.

In a conventional OFDMA-based cellular network, e.g., a wireless networkaccording to the IEEE 802.16/16e standard, incorporated herein byreference. The network confines operations to a point-to-multipointtopology, wherein only two types of network entity exist, namely basestations (BS), and mobile stations (MS). The BS manages and coordinatesall communications with the MS in a particular cell. Each MS is indirect communication with only the BS, and only the BS communicates withan infrastructure or “backbone” of the network. That is, there is onlyone hop between the MS and the BS. All communications between the MSmust pass through the BS. Furthermore, there is one connection betweenthe BS and each MS.

Due to significant loss of signal strength along the connection forcertain spectrum, the coverage area of wireless service is often oflimited geographical size. In addition, blocking and random fadingfrequently results in areas of poor reception, or even dead spots.Conventionally, this problem has been addressed by deploying BSs in adenser manner. However, the high cost of BSs and potential increase ininterference, among others, render this approach less desirable.

In an alternative approach, a relay-based network can be used. Thisnetwork includes multiple mobile stations (MS) and/or subscriberstations (SS). A relatively low-cost relay station RS extends the rangeof the BS. Some of the stations can communicate directly with the BS.Other stations can communicate directly with the RS and indirectly withthe BS. Obviously, communications on the link between the RS and BS orbetween two adjacent RSs (i.e., relay link) can become a bottleneck.

It is recognized that new functions need to be provided for protocolsoperating on links in mobile multihop relay (MMR) networks. For example,traffic forwarding and routing now becomes essential at a relay station(RS) because multiple hops can exist between the source and destinationof the traffic. Moreover, new quality of service (QoS) and securitychallenges have to be addressed properly in the MMR network.

Unfortunately, the legacy format of the media access (MAC) protocol dataunit (PDU) specified by the IEEE 802.16e standard is highly restrictiveand rigid, and cannot be used without any extension or modification tosupport such a wide variety of needs particular for networks designedaccording to the IEEE 802.16j standard.

As a result, a proper format is needed for MAC PDU on relay link.

SUMMARY OF THE INVENTION

The invention provides a data structure embodied in a computer readablemedia. The data structure is a protocol data packet (PDU) communicatedin a mobile multihop relay network between stations. The data structureincludes a relay media access header, a payload and an optional cyclicalredundancy checksum for the protocol data unit, and an indicationwhether the PDU is a relay media access protocol data unit or not.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of a format of relay MAC PDU according to anembodiment of the invention.

FIG. 2 is a block diagram of a format of a relay MAC PDU header whenpayload is included according to an embodiment of the invention;

FIG. 3 is a block diagram of a format of a relay MAC PDU header whenpayload is included according to an embodiment of the invention;

FIG. 4 is a block diagram of a format of relay MAC PDU header whenpayload is included according to an embodiment of the invention; and

FIG. 5 is a block diagram of a multihop mobile relay (MMR) networkaccording to an embodiment of the invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Definitions

For the sake of clarify and description of the invention, the followingterms are defined and used accordingly herein.

Base Station (BS)

Equipment to provide wireless communication between subscriber equipmentand an infrastructure or network backbone.

Subscriber Station (SS)

A generalized equipment set to provide communication between thesubscriber and the base station (BS).

Mobile Station (MS)

A wireless transceiver intended to be used while in motion or atunspecified locations. The MS is always a subscriber station (SS) unlessspecifically specified otherwise.

Relay Station (RS)

A wireless transceiver whose function is to relay data and controlinformation between other stations, and to execute processes thatsupport multi-hop communications.

Connection

At a physical layer, a connection runs from an RF transmitter of astation via one or more transmit antennas through a wireless channel toan RF receiver of another station via one or more receive antennas.Physically, the connection communicates RF signals using a predeterminedset of subchannels and time slots. At a logical layer, the portion ofinterest of the connection runs from a media access layer (MAC) of aprotocol stack in the transmitter to the media access layer in thereceiver. Logically, the connection caries the data and controlinformation as a single bit stream.

MAC Service Data Unit (MSDU)

A set of data specified in a protocol of a given layer and including ofprotocol control information of that layer, and possibly user data ofthat layer.

MAC Protocol Data Unit (MPDU)

A protocol data unit of a given layer of a protocol including theservice data unit coming from a higher layer and the protocol controlinformation of that layer. A burst is a sequence of contiguous MPDUsthat belong to the same connection.

Network Structure

As shown in FIG. 5 for one embodiment of the invention, a networkcommunicates packets from a set of mobile stations (MS) to a relaystation (RS) using a set of connections (C1, C2, C3). There is oneconnection between each mobile station and the relay station. The relaystation and a base station (BS) using a single connection 210 tocommunicate the packets. The BS can also communicate with other MS andSS using direct connections C4 and C5. The BS can communicate with aninfrastructure 500. All the stations and the infrastructure 500 includecomputer readable media or memory 501 for storing the data structuresaccording to the embodiments of the invention.

The packets can be communicated using OFDMA, which uses a predeterminedset of frequencies and time periods. Time is partitioned into contiguousframes. Each frame can include a downlink (DL) and an uplink (UL)subframe. The basic unit of resource for allocation is a slot, whichincludes a number of OFDMA symbols in the time domain, and onesubchannel in the frequency domain.

For clarity, herein, we refer to the MAC PDUs transmitted on relay linksas relay MAC PDUs.

The format for the relay MAC PDU according to the embodiments of ourinvention is described below. Note that a relay MAC PDU can use therelay MAC PDU format, as exemplified below. A tunnel PDU is sent withina tunnel, and contains one or multiple MAC PDUs that follow theconventional IEEE 802.16e standard format and is collected from theaccess link. A PDU is sent on a relay link, which follows theconventional IEEE 802.16e standard format. Such a MAC PDU is becollected from the access link, or is generated by a RS. A PDU is senton a relay link, which follows the relay MAC PDU format according to theembodiments of the invention. Such a MAC PDU is generated directly by aRS.

As described above, it is possible for MAC PDUs that follow theconventional IEEE 802.16e standard format and relay MAC PDU formatdescribed herein to coexist on relay links. Therefore, it is requiredthat the relay MAC PDU format and the conventional IEEE 802.16e standardformat is unambiguously distinguished on relay links.

In addition, the proposed relay MAC PDU format should be versatileenough to support a wide variety of new functions introduced in the IEEE802.16j on relay link.

Furthermore, the relay MAC PDU format should be flexible enough forfuture extension.

The data structure or format of the relay MAC PDU is stored incomputer-readable medium at any station that transmits or receives therelay MAC PDU. The data structure defines structural and functionalinterrelationships between the data structure and the computer softwareand hardware components in the stations and infrastructure 500, whichpermit the functionality of the data structure to be realized.

Relay MAC PDU Format

FIG. 1 shows the format of a relay MAC PDU 100 according to anembodiment of the invention. The MAC PDU includes a relay MAC header110, a payload 120, and an optional cyclic redundancy check (CRC) 130.In one format, the payload 120, depending on the header 110, can includesubheaders 121, and MAC PDUs 122. The relay MAC subheaders are optional.These can be used to convey information needed by a wide variety ofsignaling and management function, e.g., QoS, security, routing. Inanother format, the pay load is a management message type 125 andmanagement message 126.

Relay MAC Header Format

FIGS. 2-4 show various formats. Because of the large number of fieldsthe reference numerals have been omitted for clarity. The meanings ofthe terms are self explanatory or defined in the referenced standard.

FIG. 2 shows the format for the MAC PDU header 110 when payload isincluded. The header includes the following fields: header type (HT),reserved (RSV), relay mode indication (RMI) 201, reserved (RSV),extended subheader field (ESF), reserved (RSV), length (LEN), CID, andheader check sequence (HCS). The RMI bit 201 indicates whether thisprotocol data unit is a relay media access control protocol data unit ornot.

The one bit HT field can be used to indicate whether the MAC PDUcontains payload or not, similar to the HT bit in the conventional IEEE802.16e standard MAC PDU header. Note that since the relay MAC headerdefined herein only applies for the relay MAC PDU with payload, the HTbit in the relay MAC header essentially always has the value of 0.

The relay mode indication (RMI) bit 201 is used to distinguish the relayMAC PDU according to the invention from a conventional 802.16e MAC PDU.More specifically, if RMI bit is set to 1, the header shall follow therelay MAC header format described herein. Otherwise, if RMI bit is setto 0, the header shall follow the 802.16e generic MAC header format.Meanwhile, note that this bit was used in 802.16e generic MAC header toindicate whether mesh subheader would appear after the generic MACheader. So, if an 802.16j capable station (e.g., MS, RS, BS) isoperating in a mobile multihop relay network, this bit in the relay MACPDU header shall be interpreted as a relay mode indication bit.Otherwise, if a station is a conventional 802.16d/16e station or itoperates in a conventional 802.16d/16e network, then this bit shall beinterpreted as a mesh subheader bit.

For relay MAC PDUs that contain some payload, these PDUs are forwardedby the RS to the destination. To support various routing design, therelay MAC PDU header can contain a tunnel CID or basic CID of a RS.Given the range of CID value, RS is able to determine whether it is atunnel CID or a basic CID.

The header format for relay MAC PDU shown in FIG. 2 is further describedin Table 1.

TABLE 1 Format of Relay MAC PDU Header Syntax Size Notes MAC Header( ) {HT 1 bit if (HT == 0) { Reserved 1 bit Currently reserved. Content issubject to further discussion RMI 1 bit Mesh subheader/Relay modeindication When the value of MAC version TLV is less than 6, this is amesh subheader bit 1 = mesh subheader is present, 0 = mesh subheader isabsent When the value of MAC version TLV is 6, this is a relay modeindication bit 1 = relay MAC header is used, 0 = generic MAC header isused. Reserved 5 bits Currently reserved. Content is subject to furtherdiscussion ESF 1 bit Extended subheader field. If ESF = 0, the extendedsubheader is absent. If ESF = 1, the extended subheader is present andwill follow the GMH immediately. The ESF is applicable both in the DLand in the UL. Reserved 4 bit Currently reserved. Content is subject tofurther discussion LEN 11 bits CID 16 bits May be tunnel CID or basicCID of the RS HCS 8 bits Header check sequence } else if (HT == 1) { Ifno payload is attached Use legacy 802.16e 39 bits or 802.16j Format HCS8 bits } }

There are totally 10 bits in the relay MAC header that have been set to“reserved”. The meaning of these bits can be further defined to supportvarious new functions, such as CID encapsulation, trafficprioritization, etc., in a mobile multihop relay network.

For example, as shown in FIG. 3, the 7^(th) bit in the relay MAC header,which is set to “reserved” now, can be used to indicate whether CIDencapsulation (CE) is used nor not in the relay MAC PDU. Another exampleis to use 3 bits (11^(th) to 13^(th) bit) in the header to indicate thepriority of the associated relay MAC PDU.

Since a relay MAC PDU may contain multiple 802.16e MAC PDUs, the lengthfield may need to be extended. If that is the case, we can expand theLEN field leftward by 1 bit to make it 12 bits in the relay MAC PDUheader. Thus, the maximum total length of a relay MAC PDU supported bythe length field becomes 4096 bytes, which should be sufficient tosupport the aggregation of most types of the traffic. Then, the priorityfield has to be shifted leftward by 1 bit accordingly, as shown in FIG.4.

Besides the new features described above, the relay MAC PDU headerresembles the conventional MAC header as defined in the IEEE 802.16estandard.

Although the invention has been described by way of examples ofpreferred embodiments, it is to be understood that various otheradaptations and modifications can be made within the spirit and scope ofthe invention. Therefore, it is the object of the appended claims tocover all such variations and modifications as come within the truespirit and scope of the invention.

We claim:
 1. A station in a mobile multihop relay network comprising:memory for storing a data structure, the data structure being a protocoldata packet for communication in the mobile multihop relay network, thedata structure comprising: a relay media access control (MAC) header, apayload and an optional cyclical redundancy checksum for a protocol dataunit (PDU), in which the relay MAC header further comprises a headertype field, a first reserved bit field, a relay mode indication field, asecond reserved bit field, an extended subheader field, a third reservedbit field, a length field, a connection identifier field, and a headercheck sequence field, and wherein the five bits that immediately followthe relay mode indication bit constitute the second reserved field,wherein one of the reserved fields can indicate whether connectionidentifier encapsulation (CE) is used or not in the relay MAC PDU; and atransceiver for reading the relay mode indication field to determinewhether the PDU is a relay MAC PDU or not, wherein the transceivertransmits the protocol data packet based on the determination.
 2. Thestation of claim 1, in which the payload further comprises zero or moreextended subheaders, zero or more subheaders, zero or more IEEE 802.16eMAC PDUs, and zero or more relay MAC PDUs.
 3. The station of claim 1, inwhich the first bit in the relay MAC header is a header type field usedto indicate whether this MAC PDU has payload or not.
 4. The station ofclaim 3, in which the header type field is always set to a value thatindicates that this MAC PDU has payload.
 5. The station of claim 1, inwhich the bit that immediately follows the header type field constitutesthe first reserved bit field.
 6. The station of claim 1, in which thebit that immediately follows the first reserved bit field is the relaymode indication field, when the station involved in the communicationsupports IEEE 802.16j standard communications.
 7. The station of claim6, in which the relay mode indication field indicates whether this MACheader abides with generic MAC header format defined in the IEEE802.16d/802.16e standard.
 8. The station of claim 7, in which the relaymode indication field indicates that this MAC header abides with genericMAC header format defined in the IEEE 802.16d/802.16e standard, when therelay mode indication field is equal to
 0. 9. The station of claim 7, inwhich the relay mode indication field indicates that this MAC headerabides with relay MAC header format, when the relay mode indicationfield is equal to
 1. 10. The station of claim 1, in which the bit thatimmediately follows the first reserved bit field is the mesh subheaderfield, when the station involved in the communication only supports theIEEE 802.16d/802.16e standard.
 11. The station of claim 1, in which thebit that immediately follows the second reserved field is the extendedsubheader field bit, which is used to indicate whether there is anyextended subheader after this relay MAC header or not.
 12. The stationof claim 1, in which the four bits that immediately follows the extendedsubheader field bit constitute the third reserved bit field.
 13. Thestation of claim 12, in which three consecutive bits of the four-bitthird reserved field are used to indicate the MAC PDU.
 14. The stationof claim 1, in which the eleven bits that immediately follow the thirdreserved field constitute the length field, which is used to indicate atotal length in bytes of the MAC PDU.
 15. The station of claim 14, inwhich the eleven-bit length field is extended leftward by one bit to betwelve bits, and represents a longer size of the MAC PDU.
 16. Thestation of claim 1, in which the sixteen bits that immediately followthe length field is the connection identifier field, which contains theconnection identifier of the connection belonging to the MAC PDU. 17.The station of claim 1, in which the eight bits that immediately followthe connection identifier field is the header checksum field, whichcontains a checksum of the relay MAC header.